Downhole and temperature measuring gauges have been used for a considerable number of years in downhole well operations to measure temperature and pressure conditions in a wellbore. In one type of pressure measurement the pressure gauge is suspended by a wireline cable in a wellbore which does not typically create adverse conditions for the pressure gauge. However, in typical instances where pressure and temperature measurements are made during a drill stem test, or upon completion of the wellbore by perforation, the gauge is subject to hydraulic pressure surges and downhole shock effects in the pipe string. It is important that the pressure and temperature information or data is accurately obtained for the evaluation of the oil reservoir and productivity of a producing oil sand and thus protection of the pressure gauge against hydraulic surges or shock effects in a pipe string is highly important.
For a drill stem test, the drilling operations are temporarily discontinued when the drilling has reach a desired depth and a drill string containing a packing device, testing valves and a pressure and temperature measuring system are lowered into the open wellbore. The wellbore is packed off or sealed by the packing device, and the pressure below the packer device is measured before opening the testing valves.
Next, the testing valves are opened and during the open period of the valves and after the testing valves are closed, the pressure and temperature of the fluids in a wellbore are measured. Because the formations below the packing device are typically opened to atmosphere or low pressure, downhole pressure surges are quite common.
In a perforating operation, the pressure and temperature guage is typically mounted below a production packer (although occasionally the gauge is disposed above the packer) and lowered into the wellbore where the casing packer is set in the casing. Thereafter, a perforator may be lowered through and below the tubing string to perforate the casing and earth formations below the set packer. Alternatively, the perforator may be attached to the pipe below the packer and run in with the packer. Upon detonation of the perforator, considerable shock forces are generated downhole in the string of pipe supporting the gauge by the explosive nature of the perforator and high pressure surges are developed in the existing fluid below the packer. Thus, the pressure and temperature gauge is subjected to shock forces and surge pressures induced by the perforator. The pressure and temperature guage prior to perforation of the earth formations measure the existing pressure in the wellbore and the subsequent pressure after perforations of the well casing as a function of time.
While running a pressure gauge into a wellbore on a string of tubing the tubing is moved through the fluid in the wellbore. Thus pressure surges are incurred by the pressure gauge by virtue of the running operation of tubing and shock can be encountered if the tubing engages any ledges or shoulders in the borehole.
With the advent of highly sensitive pressure measuring devices utilizing quartz transducers the transducer occasionally can fail or malfunction because of the pressure surge or shock forces in excess of the transducer shock mounting in the pressure guage. This failure can occur typically during running in of a casing into a wellbore, during drill stem testing or upon the firing of a perforator in a wellbore.